FS 005| The Science Behind Pressure Frying

Have you ever wonder how fried chicken joints like KFC, Popeye's, and Chick-fil-A create a consistent product that's juicy and tender?

Part of their secrete lies in a specialty piece of equipment called a pressure fryer.

The pressure frying story begins during the great depression, with a man named Harland Sanders selling his southern fried chicken at a roadside stand in Corbin, Kentucky. He eventually made enough money to open up his own brick-and-morter restaurant, where his fried chicken amassed a fairly large and loyal following.

But even with his success, Mr. Sanders had one major issue; his southern fried chicken took 35 minutes to cook from start to finish.

With the classic, southern fried chicken technique, a cast iron pan or dutch oven is filled with a shallow amount of cooking oil, usually just enough to cover the bottom and the sides of the product being fried. The chicken is placed in the hot oil, flipped once, twice, maybe a few times depending on the cook, until it's golden brown on all sides and fully cooked through.

This is in contrast to deep fat frying, in which the chicken is fully submerged in hot oil, allowing it cook faster, but an approach Mr. Sanders felt was far inferior to chicken fried in the classic southern style.

How does a pressure cooker work?Sanders eventually discovered a novel solution to his problem when he attended a pressure cooking demonstration. The demonstrator explained that a tight fitting lid is applied to the pot, and when the pressure builds, the boiling point of any water based liquid contained in the pot will rise, allowing the vegetables to cook faster.

After seeing the demonstration, Sanders thought he could apply this same concept to his southern fried chicken, allowing it to not only cook faster, but possibly even end up with a better end product.

So Sanders hit the drawing board and came up with a rough working model for pressure frying chicken--his first pressure fryer was in fact a modestly tweaked version of a standard pressure cooker.

In his new, novel approach which sanders coined "pressure frying," he would start by heating cooking oil to 350-400F/176-204C in the base of a pressure cooker. Enough chicken was placed in the hot oil to allow rapid browning, while simultaneously dropping the oils temperature to around 250-275F/121-135C. The pot was sealed with a lid, and pressure was allowed to build to 15 PSI, causing water's boiling point to be raised from 212F/100C (at sea level) to 250F/121C.

Once pressure was achieved, the chicken was cooked through, which took about 8 minutes according to Sanders initial patent filing.

The pot was then vented, the chicken drained, and served.

The History of Pressure FryingHowever, this method had one major pitfall -- using a modified pressure cooker for frying was extremely dangerous. The seals could fail, pressure could build too rapidly, and there are even stories of pressure fryers blowing up in the early days of their use (no note on the casualties though).

Sanders decided to finance the development of a commercial pressure fryer, and Winston Shelton submitted the winning design. This new piece of technology, along with a Sanders' secretive eleven herbs and spices blend, spawned the culinary fast food giant Kentucky Fried Chicken, making Sanders a wealthy man, and most importantly, earning him the honorary title of Kentucky Colonel, which he attached to his name for the rest of his life.

As for Winston Shelton, his company Winston Industry became famous for the "Collectramatic" pressure fryer that is still manufactured and sold today, and would later become a hero to fast food chains and fine dining chefs alike for his invention of the C-VAP water oven.

How Does Pressure Frying Work?

How does a pressure fryer work?Pressure frying works by increasing the atmospheric pressure inside the enclosed fryer. Increased atmospheric pressure causes the boiling point of water, in this case the liquid in the fried chicken, to rise. This has a couple of effects.

First, when any product is dropped into hot oil for deep frying, the moisture at the surface quickly heats to the boiling point, causing it to evaporate as steam. This is why aggressive bubbling is seen in the early stages of frying.

But because so much steam is enveloping the fried food during the cooking process, the steam will initially act as a temperature buffer, creating a zone small zone around the product that will initially however around 212F/100C, the maximum temperature of steam at sea level.

Yet when pressure is allowed to build in the fryer, the temperature of the steam will also rise, and because it's in direct contact with the surface of the protein being fried, the protein will arrive at its finished internal temperature much faster.

Second, because the boiling point of water is raised under pressure, less of the protein's liquid (juices) turn to steam in a pressure cooker, leading to more moisture retention, and a juicier end product.

Finally, because less water is released during the frying process, the oil will actually last longer. This is because water will cause hydrolysis in oil at temperatures above 300F/149C (Chemistry of Deep-Fat Frying Oils). Hydrolysis breaks down the fatty chains that make up the frying oil, and part of the byproduct of this reaction is the formation of free form fatty acids. The more free form fatty acids an oil or fat contains, the lower it's smoke point will be.

Why Modern Pressure Fryers Cook at a Lower Temperature

If you read through Colonel Sanders' original US patent filing, he explains that after his chicken was browned, it would be cooked at 15 PSI, or 250F/121C (the boiling temperature of water under fifteen pounds of pressure per square inch at sea level).

But with modern pressure fryers, chicken is usually cooked at around 5 PSI, or only 223F/106C.

This is because in 1966 when Colonel Sanders developed his pressure frying technique, the chickens were much tougher; they were butchered 10 weeks older than the chickens we consume today.

Older chickens means more collagen (chewy connective tissues), which means a longer cook time and/or a higher temperature is necessary to make the chicken tender.

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There are 19 Comments

BBQplaya's picture

Cool episode

j..weinstein's picture

.Jacob@15.41"all about execution"
Great analogy re lack of lamb. Pretty cool for you to be frank too, it gives me an insight into the workings of a fine dining establishment.
 
On that note, I've a very interesting question.
Hypothetical situation,
You, me and Colonel Sanders are chilling in your kitchen. Staff training isn't an issue because the Colonel knows how to use a pressure fryer. Scratch that, nothing is an issue, time nor staff. However, I'm still keeping the Colonel there as that's kinda cool.
 
Naturally, with all that culinary talent present (I include myself in making that statement), we would want to make the best naked buffalo wings possible.
 
Would we do A or B,
A-Do some combination of double cook/fry
B-Do a single pressure fry
 
Why did you choose one over the other?

If I had of enjoyed learning in school this much, I'd be a rich man now.

j..weinstein's picture

In bed about to fall asleep and just had a brainwave.
Cracked open the laptop,
Boom, lets do this,

Ok, I remember  a man-v-food episode,
From 1.08min to 1.30min, 
https://www.youtube.com/watch?v=Iwf9A65vipA

They talk about locking in the juices through pressure frying, it seals the chicken and locks in the juices.

1. (double fry)--
-tonnes of gelatin at bottom of pan post precook
-gelatin contains a lot of the chicken juices
-great for sauces

2. Pressure fry(single fry)
-No gelatin in fryer base
(Mind you, single open fry yields no gelatin either)

In a nutshell,
-Does a single pressure fry hep retain those juices within the chicken thus giving a better flavour?

PS:  I totally agree with the uses and  benefits of the gelatin.
However, nobody ever asked Jacob the following,
Is the benefit of gelatin re sauces at the expense of the chicken.
I know that twice fry chicken will still be great but we want perfection.

Well, perfection is subjective. I think we can all agree that we want the knowledge necessary to define our version of perfection.

j..weinstein's picture

In the video, Jacob discusses the raised boiling point. Jacob made reference to the raised boiling point surrounding the chicken while under pressure.

While a raised boiling point is related to internal temperature,
The word surrounding seemed interesting to me.
I then wondered if pressure frying was related to the crisp skin.

My question is,
-Does the raised boiling point influence crispness?
-Will chicken skin crisp more easily during pressure fry?
-Does this mean pressure frying can be done at a lower temperature?
 (For example, standard open fry temp seems to be 375F, pressure fried seems to be 360F.) 
-If it is true that pressure frying requires lower temperatures, is this related to collagen conversion, internal moisture loss or crisping of skin?
 

Robsous's picture

Dude, too funny but awesome questions. I was thinking of buying a pressure fryer in future.

Energy costs: Pressure fryer -v- Normal fryer
I watched a henny penny pressure fryer sales video on youtube. The demo chef said that you would save on energy costs because the fryer falls to idle mode between cooks.

A normal fryer is held at 375F between cooks
A pressure fryer falls to 250F between cooks

My argument,
-If  a normal fryer is at 375F, there's really no heat up going on. The green light stays on all the time. I know it's at 375F but it doesn't require energy to stay there.

-A pressure fryer falls to 250F but it has to heat all the way up to 375F for each cook. Surely a pressure fryer has more oil costs?

Robsous's picture

High temperature is responsible for flavor
Regarding your question about pressure frying requiring a lower temperature.
I know your comments were in relation to crisp skin.

I do remember hearing that high temperature is responsible for flavor.
So I always assumed that high temps gave better flavor.

The article was in relation to fried chicken.
Every fried chicken breading recipe contains spices.
Maybe it was related to the activation of flavor in the spices?

What you think of the above Jacob, is it just malarkey?

jacob burton's picture

Here's an audio response. Sorry Robsous, but I didn't see your question till after I hit record. Will answer tomorrow.

Holly's picture

Hey..... I thought I was best in class when I recommended that Jw should do a single fry in his pressure fryer. Now, you're saying not so...

I thought your video made perfect sense as to how one could complete the two stages in cook.

What about frozen par-cooked jumbo wings, your pressure fryer might work on them as they will take longer to cook?

@jw
Post your results because they don't seem to do any domestic pressure fryers.
 

Holly's picture

How will raised temperature result in mushy / falling apart?

I thought the raised boiling point elongated the time require to reach boiling point thus retaining moisture in wing?

I never knew that raised internal boiling cause overcooking, I thought it prolonged the cook time available without drying out?

 
Mushy, what is science behind mushy?
j..weinstein's picture

I was going to ask Holly's question with regard to Jacobs quote  "a pressure fry will cook too rapidly to control temperature".

KFC pressure fry their hot wings for about 6 minutes.
They are egg washed and breaded if that makes a difference.

Does the breading safeguard the wing from the pressure fry?
 
 
jacob burton's picture

The boiling point of water in a pot is limited by atmospheric pressure. This means there is a limit to how hot something can get without being pressurized. Now if the boiling point of water is raised, there's more heat, which means things cook faster.

The collagen in chicken wings starts to break down at a temperature far below boiling (155F). So when a chicken wing or anything else is cooked under pressure, the "heat limit" of boiling water is raised, allowing the product to cook faster than normal.

If too much collagen breaks down, you get a mushy wing.

@ J..weinstein,

Breadings are for flavor and texture, and/or to provide a protective coating to something without skin (fish, vegetables, whatever). If you were getting good results at KFC with a 6 minute fry, then that sounds like a good starting point for testing. I understand how pressure fryers work, but I don't have one at my disposal, so I can't test any or your ideas, which I would need to do to give you a definitive answer.

The best thing I can suggest is to do some testing on your end with the pressure fryer, and I can help you explain the science behind your results, which can inform future tests and procedures.

Robsous's picture

@Jw

Post results on the Pressure fryer. I want to hear about them as I always wanted a pressure fryer.  Sounds like the possibilities are endless regarding wings.

Jacob can only take us so far on this one brother, you're the lucky one with the pressure fryer.

j..weinstein's picture

Hey Jacob, just came across this video again on youtube. Has to be one of the best you've done.

Jacob "Less moisture from the product is evaporated leading to juicier meat"

Does a raised boiling point somehow directly maintain moisture or is it juicier based on a shorter cook time alone?

jacob burton's picture

Exactly.

Raising the boiling point means less water evaporates during cooking. At the same time, collagen breaks down faster due to the raised boiling point of the water. Just like braising a short rib using the classic technique will take about 4 hours, and pressure cooking the short rib will take 90 minutes.

j..weinstein's picture

I think you'll understand my hypothesis below. 

Jacob"Meat cooks faster, as liquid is hotter" (I assume that's liquid within the meat)

Internal meat temperature is elevated in accordance with a raised boiling point. Although both temperatures are elevated when frying under pressure, the temperature gap between internal meat temperature and boilng point is actaully the same in both pressure frying and open frying.

As the temperature gap between internal meat and boiling point is the same in both open and pressure frying. It's difficult for me to ascertain how a raised boiling point directly maintains juices.

j..weinstein's picture

Yeah, that's cool. My fault, I got into one of those intense moments. I regretted posting it.

Your audio above and the video are both excellent. Best resources online by far with regard to pressure frying. I've studied them both in detail.

Basically, I just can't see why a raised boiling point retains meat juices. I know it's true, it's just bugging me how I can't understand the mechanics. You've explained it umpteen times, just annoyed at myself.

jacob burton's picture

No worries, I just didn't really understand what you were asking. Now I do.

"I just can't see why a raised boiling point retains meat juices."

It does seem counter intuitive, but, when you raise the boiling point of water, it will take more heat energy to turn that water into to steam. Once the water turns to steam it starts to evaporate into the atmosphere, never to be seen again. So in the case of pressure frying, higher boiling point equals less water evaporation which means a juicier end product.

Also, think of the boiling point of water as a universal speed limit for cooking food. At sea level, that speed limit is 212F/100C. When placing a pot under pressure, thus raising the boiling point of water, the speed limit is raised, which allows food to be cooked faster.

Hope that makes sense.

j..weinstein's picture

It does brother,

Thanks for your patience.